The present invention relates to a method and apparatus for producing rolls of thermoplastic film stock for use in manufacturing flexible containers and product packaging, and in particular, to a method and apparatus for producing rolls of zippered film.
In the production of flexible containers, such as plastic bags and product packaging, film webs are supplied to manufacturers in rolls with and without zippers attached to the web. Zippered film is supplied in a variety of configurations including a "J-folded" closed zipper configuration, so called because its cross-section resembles the letter "J". Zippered film is also supplied in open zipper, open web configurations where the film web is opened flat and zipper elements are spaced apart either along opposite edges or near the center of the open web. Each of these configurations, shown in FIGS. 1A-1C, has been developed over the years to solve particular problems with one of the many types of packaging machines, and each has its own particular advantages and disadvantages.
The advantage of the J-folded film is that the interlocked zipper elements form a structure which protects the zipper elements during winding and storage in rolls. Typically, the disadvantage of J-folded film is the need to unfold the web before forming a container on a packaging machine. This step requires special equipment to be installed in what are typically confined areas. Further, drag induced by unfolding slows down the packaging or bag making process. See Boeckmann et al, U.S. Pat. No. 4,646,511, Col. 1, line 60-Col. 2, line 4 (the '511 patent).
Conversely, open zipper, open web configurations are not folded and, thus, are ready for use. However, their primary disadvantage is that damage may occur to the zipper elements during winding of the film into rolls. When disengaged, the zipper elements are unsupported and subject to tipping when there is too much winding pressure. Subsequent winding and the pressure of additional layers injures tipped zipper elements. To avoid damaging pressures, open zipper, open web rolls must be produced in smaller diameters, requiring more frequent spool changes and greater machine down-time when used.
In addition, both J-folded and open zipper, open web configuration film rolls require an additional machine or device to manipulate the film for use on a packaging machine. Among the numerous devices developed to meet that need are those of Ausnit, U.S. Pat. No. 4,625,496; Boeckmann et al, U.S. Pat. No. 4,704,842; Wojcik, U.S. Pat. No. 4,941,307; and the '511 patent. Each discloses a process wherein, at the infeed of a packaging machine, moving J-folded or open zipper, open web films are refolded into a closed zipper, open web configuration in transition to further manipulation to form flexible containers or product packaging. Again, however, the disadvantages of these devices include their slower speed, space requirements and the additional complexity they add to equipment needed to manipulate and variously position film for use at the point of packaging.
Accordingly, an improved apparatus and method for providing film rolls to packaging machinery are needed to overcome the drawbacks of prior art practices.